During the braking phase of a landing or rejected take-off of an aircraft, the main source of retarding forces arises from the frictional contact between aircraft tires and the runway surface. These frictional forces are generated by the action of the applied brakes on the main landing gear wheels.
As conventional aircraft typically have brakes only on the main wheels (and not on the nose wheels), a key parameter that influences braking capability is the vertical load acting in the main landing gear during ground deceleration. The greater the vertical load acting on main landing gear, the higher the deceleration forces that the brakes can provide to slow and stop the aircraft.